Biological treatment such as the conventional activated sludge process or oxidation ditch process is an extremely advantageous treatment method in terms of cost in wastewater treatment because it does not require as complex equipment as methods of chemical and physical purification, generates few byproducts, and also takes less energy input. The conventional activated sludge process in particular is widely used in economically developing emerging countries because it can treat large quantities of wastewater in a short time and is relatively easy to control.
Broadly speaking, a conventional activated sludge process system consists of an aeration tank (biological treatment tank) and a settling tank. Aerobic conditions are produced in the aeration tank by blowing air into the wastewater by a blower. Microorganisms that purify organic matter are activated, and the organic matter in the wastewater is removed. The activated sludge and treated water are separated in the settling tank. The treated water of the upper layer is then removed to the outside, and released into the environment after appropriate post-treatment. The activated sludge, on the other hand, is sent back to the aeration tank to maintain the necessary microbial concentration in the aeration tank, and any excess (excess sludge) is removed to the outside and finally disposed of as industrial waste. The microorganisms in the aeration tank are the major component of the excess sludge which is a conglomerate of microorganisms that have grown using the organic matter in the wastewater as a substrate. Therefore, the volume of sludge generated also increases as the organic matter in the wastewater is removed.
On the other hand, the microorganisms utilized in such biological treatment naturally become predominant or are activated in the wastewater treatment environment. The food chain also stretches from bacteria to protozoa, and the organic matter is removed. Removal of the organic matter in wastewater therefore takes a relatively long time in biological treatment.
Improvement of the wastewater treatment speed using a method of making Bacillus, which have a rapid growth rate even among the microorganisms in the wastewater treatment environment and produce large amounts of enzymes to decompose organic matter, predominant has therefore been proposed and put to practical use. For example, the following Patent Documents 1-6 propose making Bacillus predominant in the aeration tank and conducting wastewater treatment. The following Patent Documents 7-13 also propose making Bacillus predominant and adding minerals including silicon to maintain them.